If you chain “Rare Metalmorph” to an effect like “Snatch Steal” that targets a monster, “Snatch Steal” is equipped but its effect is negated while “Rare Metalmorph” is active.
If a monster targeted by “Rare Metalmorph” is flipped face-down, it is no longer targeted by “Rare Metalmorph” and “Rare Metalmorph” remains on the field meaninglessly.